Waste printed circuit boards cannot be decomposed naturally and have to be treated with certain processes. Otherwise the environment will be seriously polluted.
The inventor of the present invention has introduced a method for treating waste printed circuit boards with molten tin or its alloy, which was filed for patent application in U.S. Patent and Trademark Office on May 5, 1998 with filing number 09/072,136 now U.S. Pat. No. 5,979,033.
The method in the last application includes the following actions.
1. The waste printed circuit boards are put into a bath containing molten tin, and the bath is located in a treating furnace. PA1 2. The waste circuit boards are crushed and the molten tin is stirred so as to remove copper foil from the circuit board, which is carbonized. PA1 3. Further stirring separates the copper foil, the thermosetting plastic, and the glass fiber from one another. PA1 4. The thermosetting plastic residues and the glass fiber, which floats on an upper surface of the molted tin, are scraped off with a scraping device, and collected in a collect tank. PA1 5. Volatile gases produced in the carbonizing process of the thermosetting plastic is burned and decomposed by a buner. The rest of the volatile gases which is not completely decomposed is led to a combustion chamber located outside the treating furnace, and then converted into stable gases. PA1 6. The copper foil is collected in a metal collect tank. PA1 1. Using tin as a heating medium makes the method cost relatively much higher due to cost of tin. PA1 2. The tin will more or less adhere to the removed copper foil and the removed glass fiber. Therefore, requiring further separation and making the same unable to be as pure as desired for recycling. PA1 (1) putting said waste circuit boards in a treating furnace; crushing and stirring the circuit boards with a crushing and stirring device for copper foil of the circuit boards to be separated therefrom, thermosetting plastic of the circuit boards being carbonized under said crushing and stirring action; PA1 (2) further stirring the circuit boards with the crushing and stirring device for the copper foil, the thermosetting plastic and glass fiber of the circuit boards to separate from one another due to difference in density; PA1 (2-1-1) scraping floating residues of the thermosetting plastic and the glass fiber which floats on upper surface of the molten mixture of inorganic salts with a floating residues scraping device; PA1 (2-1-2) collecting the scraped thermosetting plastic and the scraped glass fiber with a floating residues collecting tank; PA1 (2-2-1) destroying volatile gases produced when the thermosetting plastic is being carbonized with a burner; PA1 (2-2-2) sending part of the volatile gases which have not been destroyed into a combustion chamber, and converting same into the stable gases; PA1 (2-3-1) removing the copper foil by a certain amount regularly; and, PA1 (2-3-2) collecting the removed copper foil in a metal collect tank.
However, it is found that the method for treating waste printed circuit board with molten tin still has undesirable features as follows.